Nanomotors are an amazing feat of engineering: tiny gold rods less than a micrometer long, powered by ultrasonic waves to spin at crazy-fast speeds. How fast? Scientists just figured out a way to measure, and it's astonishing: 150,000 RPM, ten times faster than the fastest race car engine.

There's still a lot researchers don't know about nanomotors. Back in 2012, researchers at Penn State figured out that nano-size gold rods suspended in liquid will spin like tiny drill bits when ultrasound waves are applied. But because the tiny machine are so tiny, nobody ever had a way to measure just how fast they were spinning. Previous estimates put the top speed around 15,000 RPM.

Well, a new research paper published in the journal ACS Nano explains how scientists were finally able to track the screaming micro-machines. They mixed the tiny gold rods (five stacked end-to-end would measure the width of a human hair) with 400-nanometer styrofoam beads, and placed the solution between glass and silicon plates. By measuring how fast the beads move as they swirl around the rods, the scientists were able to estimate the speed of the little spinners.